Bill Richardson is closely tied with the Clinton gang. His selling point is his ability to bring in the Hispanic vote, which is not as overwhelmingly pro-Democrat as the black vote. Also, he should be able to carry his home state of New Mexico, a small prize to be sure (4 electoral votes), but lost by Kerry in 2004. As a Hispanic, he can help the ticket in the neighboring states of Colorado, Arizona, and Nevada, all of which are "light red", and perhaps Florida as well.
Why would anyone need NM, CO, AZ, NV and FL to win the presidential election?
If he is the VP Nominee it is going to be a tough race for the GOP.
The only fly in the ointment I can see is Webb's election to the Senate. If the Clintons think Webb could bring in more Southern electoral votes than Richardson can Western (and/or Florida), they might throw him over.